The present invention relates to an elevator system for vertically carrying human beings or freight, and more especially to an elevator system for transporting automobiles from one floor to the designated floor in a parking tower.
FIG. 5 shows an conventional elevator system for passengers or freight. This comprises a carriage (c), wire cable (b), counterweight (d), two wheels (a) and driving unit (e), for example, a winching machine and so on which is located in an upper elevator room. The carriage is suspended on one end of cable (b) (c) and the counterweight (d) is suspended on the other end of the cable (b). The cable (b) is threaded over the wheels (a) and the driving unit (e) in the upper elevator room at the top of the shaft. This system allows human beings or freight to be carried in the carriage (c) by the driving unit (e) winding up and down the cable (b).
This described elevator system has certain disadvantages such as the following. The requirement for the driving unit comprising a large scale electric motor, a device for changing speed and a winching machine, to be located in a vertically higher position than the rest of the system makes necessary high rigged design of structures and wide occupied space for the driving unit (e). The structure of a parking tower, which must absorb the vibrations from the driving unit, allows low efficiency of vibrations in spite of the builder taking actions to prevent noises and vibrations from occurring while running the driving unit (e). Particularly, the lighter weight of materials of construction as may be used in a structure such as a parking tower, causes this problem to be greater.
Slippage between suspended cable (b), which can be wire cable or rope, and the wheels (a) can occur and may result in a lack of accuracy and/or repeatability in definite stoppage points of the carriage (c) after going up and down. In case of using a conventional elevator system for a vehicle parking system to carry automobiles, it is conceived that an elevator system such as carriage and counterweight, respectively, tied to ends of a suspended cable are vertically moved. However, as stated above, in addition to the slippage which is apt to occur between wheel and cable in the use of wire rope for cable, there are several problems such that carriage cannot hold horizontal or it is apt to go down at one end of a pair of suspended cables. It has been considered to adopt chain instead of a suspended cable (b). However, it is difficult to keep the stability of controlling elevation to be balanced between the carriage and the counterweight in such a system, because the self weight of the suspended cable or chain is added onto the weight of the carriage when carriage goes down, and the self weight of the suspended cable is added onto the weight of the counterweight when the carriage goes up.
The self weight of the suspended cable, when added onto the weight of the carriage or counterweight, is not negligible when considering how to adjust balance between the carriage and the counterweight. This is one reason which causes trouble for the driving unit in the form of excessive overload. Often it becomes necessary to use a larger sized driving source.